Siderophore Research Articles

Efecto de Pseudomonas fluorescentes en la germinación de semilla y vigor de plántulas de jitomate

The bacteria Clavibacter michiganensis subsp. michiganensis (Cmm) and Xanthomonas vesicatoria (Xv) are of great interest in tomato production because they cause major economic losses worldwide. They are transmitted by seeds and the management strategies for these pathogens in tomato production systems are not completely effective. Therefore, the objective of this research was to identify fluorescent Pseudomonas strains of different ecological origin and evaluate their antagonism against Cmm and Xv and their effect as growth promoters on tomato seed germination and seedling vigor. We evaluated 356 fluorescent Pseudomonas strains isolated from different ecological niches: roselle (Hibiscus sabdariffa L.) rhizosphere, tomato (Solanum lycopersicum L.) rhizosphere and Claviceps gigantean sclerotium mycosphere. Antagonism against C. michiganensis and Xanthomonas vesicatoria was evaluated in in vitro dual confrontation tests in King’s B culture medium, which generated 20 fluorescent P. strains antagonistic to one or both bacteria. The antagonistic strains (n = 20) were characterized metabolically by their production of 3-indole acetic acid (IAA) and siderophores (SID), and were identified genetically by the polymerase chain reaction (PCR) technique with the amplification and sequencing of the 16S rRNA gene by primers FD1 and RD1. The results of the metabolic characterization of the strains indicated that 65 % produced IAA and 100 % SID. Inoculation of these bacteria, by the Bio-priming technique, in tomato var. Rio Grande seeds showed that 95 % of them significantly (P ≤ 0.05) increased the germination rate (T50) and the dry biomass production of the seedling roots. The partial sequencing of the 16S rRNA gene identified the bacterial strains as Pseudomonas sp. (65 %), P. putida (25 %) and P. fluorescens (10 %).

Humiron® is an effective biodegradable source of chelated iron for plants: An iron-59 uptake study

Here we tested plants' ability to use iron (Fe) from the water-soluble commercial product Humiron® (a complex of Fe with highly purified and solubilized humic acids extracted from leonardite) as a source of chelated Fe for both strategy 1 (e.g. cucumber) and strategy 2 (e.g. barley) plant species grown under low Fe conditions. Iron from radioactive 59Fe-labelled Humiron® can easily be acquired by strategy 1 plant species via reduction of FeIII by the inducible plasma membrane-bound reductase, similarly to the reduction of synthetic FeIII-chelates. Strategy 2 plant species can also efficiently utilize Fe from Humiron® via ligand exchange between humates and phytosiderophores (PS). Moreover, the efficacy of Humiron® is comparable to Fe complexed with waterextractable humic substances obtained form peat. Being easily biodegradable this product can be used as an effective Fe source for organic crop production.

Pathotyping of diarrhoeagenic cattle Escherichia coli strains isolated in the Province of Tehran, Iran.

An oligonucleotide DNA microarray targeting 348 virulence factors and genetic markers was used in the pathotyping, serotyping and phylogrouping of 51 Escherichia coli strains isolated from faecal samples. The samples were collected from diarrhoeic 1 to 30 days old calves located at 14 farms in the Tehran province, Iran. Positive microarray signals for genes encoding the Locus of Enterocyte E acement (LEE), the Type III Secretion System (TTSS), and the absence of EPEC adherence factor (EAF) permitted the pathotyping of 25 strains as atypical Enteropathogenic (aEPEC) or Enterohaemorrhagic Escherichia coli (EHEC). The lack of LEE and TTSS-associated genes distinguished the remaining 26 strains, which were classi ed as Extraintestinal pathogenic E. coli (ExPEC). Atypical EPEC belonged to phylogroup B1 and possessed a LEE pro le tir-1, eae(beta), espA-1, espB-3. The EHEC strains primarily belonged to the B1 phylogroup type-O26 and possessed either a LEE pro le tir-1, eae(beta), espA-1, espB-3, or a B1 type-O111, LEE tir-3, eae(gamma), espA-1, espB-2. ExPEC-typed strains generally harboured genes localised to the constant region of Colicin V plasmid (pColV), including increased serum survival factor (iss), complement resistance protein (traT), aerobactin operon (iucD), and the siderophore receptor (iroN). The microarray platform used in this study is well suited to accurately and rapidly type attaching and e acing E. coli (AEEC-types), thus providing a database for the meta-analysis of ExPEC-typed strains.

Phytosiderophore-induced mobilization and uptake of Cd, Cu, Fe, Ni, Pb and Zn by wheat plants grown on metal-enriched soils

We investigated to which extent phytosiderophores (PS), released by grasses for the acquisition of iron, solubilize other metals in contaminated soils, and how this affects metal mobilization and uptake in wheat plants. A plant-based bioassay (‘RHIZOtest’) and batch extraction scheme were carried out for assessing metal mobilisation in soil, PS exudation and metal accumulation in wheat. Increased PS exudation was observed in Fe-deficient wheat, leading to enhanced Zn, Cu, Mn and Ni concentrations in wheat shoots on some soils. In contrast, plant Cd and Pb concentrations were not affected. Likewise, in the batch experiment, strongly increased extractable Cu, Ni and Zn concentrations were observed, in particular when 100 or 1000μM PS were added. Our results suggest that Fe deficiency can enhance the accumulation of some metals in shoots of grass species. Although our results indicate that the risk of enhanced accumulation of Cd and Pb in Fe deficient wheat shoots is rather small, further experiments conducted on soil for the complete vegetation period would be needed to confirm this observation.

EXPLOITATION OF PROMISING NATIVE STRAINS OF BACILLUS SUBTILIS WITH ANTAGONISTIC PROPERTIES AGAINST FUNGAL PATHOGENS AND THEIR PGPR CHARACTERISTIC

Fifteen Bacillus subtilis strains which produced antifungal substances against plant pathogens i.e. Fusarium oxysporum f. sp. melonis, Rhizoctonia solani (RRS1) and Rhizoctonia solani (PRS1) were characterized biochemically and screened in vitro for their plant growth promoting traits as indole acetic acid (IAA), siderophore and hydrogen cyanide (HCN) production, as well as their antagonistic activity. In dual culture assays B. subtilis strains implicated decreased growth of F. oxysporum f. sp. melonis (upto 85.5%) causing muskmelon wilt, R. solani (RRS1) (upto 73.7%) causing sheath blight of rice and R. solani (PRS1) (upto 82.5%) causing black scurf of potato. The production of indole acetic acid (IAA) by all rhizobacteria was investigated as important mechanism for plant growth stimulation. Maximum in vitro IAA values were producedby B. subtilis FDK-21L (7.0 µg/ml) by addition of Ltryptophan in the culture medium. B. subtilis FDK-21L presented high activity of siderophore production. Diameter of halo varied from 0.4 to 3.2 cm on CAS agar plates. FDK-21L showed significant reduction of muskmelon wilt incidence (65.7%), disease severity of sheath blight of rice (70.8%) and black scurf of potato (97.2%). As B. subtilis FDK-21L exhibited several traits beneficial to the host and showed promising results when applied as bioinoculant, it may be used to develop new, safer and effective formulation as an alternative to chemical fungicides.

Transcriptional and physiological analyses of Fe deficiency response in maize reveal the presence of Strategy I components and Fe/P interactions

BackgroundUnder limited iron (Fe) availability maize, a Strategy II plant, improves Fe acquisition through the release of phytosiderophores (PS) into the rhizosphere and the subsequent uptake of Fe-PS complexes into root cells. Occurrence of Strategy-I-like components and interactions with phosphorous (P) nutrition has been hypothesized based on molecular and physiological studies in grasses.ResultsIn this report transcriptomic analysis (NimbleGen microarray) of Fe deficiency response revealed that maize roots modulated the expression levels of 724 genes (508 up- and 216 down-regulated, respectively). As expected, roots of Fe-deficient maize plants overexpressed genes involved in the synthesis and release of 2’-deoxymugineic acid (the main PS released by maize roots). A strong modulation of genes involved in regulatory aspects, Fe translocation, root morphological modification, primary metabolic pathways and hormonal metabolism was induced by the nutritional stress. Genes encoding transporters for Fe2+ (ZmNRAMP1) and P (ZmPHT1;7 and ZmPHO1) were also up-regulated under Fe deficiency.Fe-deficient maize plants accumulated higher amounts of P than the Fe-sufficient ones, both in roots and shoots. The supply of 1 μM 59Fe, as soluble (Fe-Citrate and Fe-PS) or sparingly soluble (Ferrihydrite) sources to deficient plants, caused a rapid down-regulation of genes coding for PS and Fe(III)-PS transport, as well as of ZmNRAMP1 and ZmPHT1;7.Levels of 32P absorption essentially followed the rates of 59Fe uptake in Fe-deficient plants during Fe resupply, suggesting that P accumulation might be regulated by Fe uptake in maize plants.ConclusionsThe transcriptional response to Fe-deficiency in maize roots confirmed the modulation of known genes involved in the Strategy II and revealed the presence of Strategy I components usually described in dicots. Moreover, data here presented provide evidence of a close relationship between two essential nutrients for plants, Fe and P, and highlight a key role played by Fe and P transporters to preserve the homeostasis of these two nutrients in maize plants.

The characterization of the adaptive responses of durum wheat to different Fe availability highlights an optimum Fe requirement threshold

Plant mechanisms responding to iron (Fe) deficiency have been widely described; it is well known that Strategy II plants, as durum wheat, cope with this stress by increasing both the synthesis and secretion of phytosiderophores (PS). The important contribution of the sulfate assimilatory pathway has been also demonstrated to improve Fe use efficiency in several grasses, such as maize, barley and wheat, most likely because PS are produced from nicotianamine, whose precursor is methionine.Here, the physiological response of durum wheat (T. durum L.) plants - in terms of plant ionome, PS release, thiols content and S pathway-related enzymes – was investigated by gradually decreasing Fe availability that allowed the identification of three specific limit Fe concentrations: 75 μM, 25 μM and 0 μM Fe, i.e. the complete Fe deprivation. At each limit, plants begin to induce different and specific adaptive responses to improve Fe acquisition or to reduce the damage resulting from limited Fe availability.The identification of the Fe availability level below which durum wheat plants start an expensive metabolic reorganization of S and several other elements, could be of benefit not only for an effective cultivation of the crop but also for the grain quality.

Siderophores of Haloalkaliphilic Archaea from Lonar Lake, Maharashtra, India

Under iron-limiting conditions, most prokaryotes, certain fungi and some monocotyledonous plants are known to produce low molecular weight (often <1000 Da), high-affinity chelating agents that solubilize, by sequestering ferric ion from the environment and transporting it into the cells through specific receptors. These molecules are known as siderophores and are typically found in iron-deficient cultures.

Native rhizobia from Zn mining soil promote the growth of Leucaena leucocephala on contaminated soil

ABSTRACTPlants on contaminated mining soils often show a reduced growth due to nutrient depletion as well as trace elements (TEs) toxicity. Since those conditions threat plant's survival, plant growth-promoting rhizobacteria (PGPRs), such as rhizobia, might be of crucial importance for plant colonization on TE-contaminated soils. Native rhizobia from mining soils are promising candidates for bioaugmented phytoremediation of those soils as they are adapted to the specific conditions. In this work, rhizobia from Zn- and Cd-contaminated mining soils were in vitro screened for their PGP features [organic acids, indole-3-acetic acid (IAA), and siderophore (SID) production; 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity; and Ca3(PO4)2 solubilization] and Zn and Cd tolerance. In addition, some type and reference rhizobia strains were included in the study as well. The in vitro screening indicated that rhizobia and other native genera have great potential for phytoremediation purposes, by exerting, besides biological N2 fixation, other plant growth-promoting traits. Leucaena leucocephala–Mesorhizobium sp. (UFLA 01-765) showed multielement tolerance and an efficient symbiosis on contaminated soil, decreasing the activities of antioxidative enzymes in shoots. This symbiosis is a promising combination for phytostabilization.

Effect of three safeners on sulfur assimilation and iron deficiency response in barley (Hordeum vulgare) plants.

Safeners are agrochemicals used in agriculture to protect crops from herbicide injuries. They act by stimulating herbicide metabolism. As graminaceous plants, to cope with iron (Fe) deficiency, activate sulfur (S) metabolism and release huge amounts of Fe-chelating compounds, or phytosiderophores (PSs), we investigated, in barley plants (Hordeum vulgare, L.) grown in Fe deficiency, the effects of three safeners on two enzymes of S assimilation, cysteine (Cys) and glutathione (GSH), and PS release. Finally, we monitored the root Fe content in plants treated with the most effective safener. Generally, all the safeners activated S metabolism and increased Cys and GSH contents. In addition, the safened plants excreted higher levels of PSs. Given that mefenpyr-diethyl (Mef) was the most effective in causing these effects, we assessed the Fe concentration in Mef-treated barley and found higher Fe levels than those in untreated plants. The three safeners, in different ways but specifically, activated S reductive metabolism and regulated Cys and GSH contents, PS release rate and Fe content (Mef-treated barley). The results of this research provide new indications of the biochemical and physiological mechanisms involved in the safening action. © 2016 Society of Chemical Industry.

Microbial decomposition of 13C- labeled phytosiderophores in the rhizosphere of wheat: Mineralization dynamics and key microbial groups involved

Being low molecular weight carbon (LMW-C) compounds, phytosiderophores (PS) released by strategy II plants are highly susceptible to microbial decomposition. However, to date very little is known about the fate of PS in soil. Using in-house synthesized 13C4-2′-deoxymugineic acid (DMA), the main PS released by wheat, we investigated DMA mineralization dynamics, including microbial incorporation into phospholipid fatty acids (PLFA), in the wheat rhizosphere and bulk soil of two alkaline and one acidic soil. Half-lives of the intact DMA molecule (3–8 h) as well as of DMA-derived C-compounds (8–38 days) were in the same order of magnitude as those published for other LMW-C compounds like sugars, amino acids and organic acids. Combining mineralization with PLFA data showed that between 40 and 65% of the added DMA was either respired or incorporated into soil microbial biomass after 24 h, with the largest part of total incorporated DMA-13C being recovered in gram negative bacteria. Considering root growth dynamics and that PS are mainly exuded from root tips, the significantly slower mineralization of DMA in bulk soil is of high ecological importance to enhance the Fe scavenging efficiency of PS released into the soil.

The effect of excess sulfate supply on iron accumulation in three graminaceous plants at the early vegetative phase

In recent years it has been established a significant relationship between sulfur (S) and iron (Fe) nutrition. In particular, it has been demonstrated that S deprivation can hinder Fe acquisition in barley, maize and wheat. This can be explained by assuming that, in order to cope with low Fe availability in the soil, grasses have evolved a phytosiderophores (PS)-based Fe chelation system (Strategy II) and PS are synthesized from methionine, through a nicotianamine intermediate.On the other hand, it has been demonstrated that wheat plants exhibit a higher Fe accumulation when supplied with excess S concentration, this effect being especially beneficial under severely limited Fe supply.The goal of this study was to explore whether the higher ability to acquire Fe, induced by a higher S supply, might be a general response of graminaceous species.The response of durum wheat (Triticum durum L.), barley (Hordeum vulgare L.), and maize (Zea mays L.) to the excess of S availability (2.4mM vs 1.2mM which is considered as optimal) was studied as a function of Fe availability (limited and sufficient, 20 and 80μM, respectively). At the end of the experimental period, which lasted 11 days, growth parameters (shoot and root fresh weight and chlorophyll content), total S and Fe concentrations, and PS release rate were compared among the three species. Furthermore, we evaluated plant sulfate uptake capability, by analysing the expression of genes coding for high affinity sulfate transporter (TdST1.1, HvST1.1 and ZmST1.1) in roots of each graminaceous plant.Our preliminary findings are largely consistent with the apparent divergence among the three species. In particular, an excess S supply may result in the improvement of Fe use efficiency in durum wheat plants, but not in both barley and maize.The use of higher S supply seems to be a promising approach, at least for wheat plants, which can both reduce agricultural demand for Fe fertilizers and improve the Fe use efficiency of plants.

Studies on antagonistic effect against plant pathogenic fungi from Endophytic fungi isolated from Hottuynia Cordata Thunb and screening for Siderophore and indole-3-acetic acid production

The endophytic fungi that colonizes internal plant tissues without causing apparent harm to their host were isolated from healthy leaf, root and stem of Hottuynia cordata Thunb. Twelve fungal isolates found were identified by their morphological characteristic and using molecular technique. The result showed that ten isolates belonging to Ascomycota were presumed to be in genus Colletotrichum, Lasiodiplodia and Fusarium in eight isolates and two isolates were identified to class Dothideomycetes and Sordariomycetes. Two unidentified isolates (R14 and R15), confined only to root segments were isolated, these members may be from the group of Mycelia-Sterilia. The evaluation of antagonistic activity of twelve fungal endophytes isolated from healthy Houttuynia cordata Thumb against Trichoderma harzianum and five plant pathogenic fungi (Fusarium oxysporum, Sclerotium rolfsii, Rhizoctonia sp., Alternaria brassicicola and Phytophthora palmivora) by dual culture technique were performed. The in vitro antagonistic activities as two types of activities in this study; mycoparasitism and competition were found. Endophyte isolate B06, B12, B09 and R15 gave the highest percent inhibition of radial growth against to the plant pathogenic fungi (F. oxysporum, S. rolfsii, A. brassicicola) and T. harzianum within 24.22%, 29.07%, 13.54 and 24.15%, respectively. Endophyte isolate R14 showed the highest antagonistic activity to Rhizoctonia sp. and P. palmivora with 39.33% and 33.34% respectively. For the siderophore production, the seven active endophyte isolates showed orange halo formed around the colonies more than 30 mm on CAS agar. Three endophyte isolates efficiently produced IAA more than 24 µg/ml. The active endophyte isolates B06 identified as Lasiodiplodia pseudotheobromae showed the highest ability to produce IAA (37.034 µg/ml) and also showed the highest orange halo formed around the colonies which determined to siderophore production.

Retention of phytosiderophores by the soil solid phase - adsorption and desorption.

Background and aimsGraminaceous plants exude phytosiderophores (PS) for acquiring Fe. Adsorption of PS and its metal complexes to the soil solid phase reduces the FePS solution concentration and hence Fe uptake. In this study we aimed to quantify adsorption, and to determine to what extent adsorption depends on the complexed metal and on soil properties. Furthermore, we examined if adsorption is a reversible process.MethodsAdsorption and desorption of PS and metal-PS complexes were examined in batch experiments in which the PS 2′-deoxymugineic acid (DMA) and its metal-complexes (FeDMA, CuDMA, NiDMA and ZnDMA) interacted with several calcareous soils.ResultsAdsorption of DMA ligand (0–1000 μM) and metal-DMA complexes (0–100 μM) was linear in the concentration range examined. Adsorption varied by a factor ≈2 depending on the complexed metal and by up to a factor 3.5 depending on the soil. Under field-like conditions (50 % water holding capacity), 50–84 % of the DMA was predicted to be retained to the soil solid phase. Alike adsorption, desorption of metal-DMA complexes is fast (approximate equilibrium within 1 hour). However, only a small fraction of the adsorbed FeDMA (28–35 %) could be desorbed.ConclusionsDespite this small fraction, the desorbed FeDMA still exceeded the amount in solution, indicating that desorption of FeDMA from soil reactive compounds can be an important process buffering the solution concentration.Electronic supplementary materialThe online version of this article (doi:10.1007/s11104-016-2800-x) contains supplementary material, which is available to authorized users.

HOMOLOGY MODELING AND TOPOLOGY PREDICTION OF FRPBPROTEININ NEISSERIA MENINGITIDIS

Iron is an essential nutrient for almost all bacteria, but the concentration of free iron in the human host is too low to support growth. In the extracellular compartments of the human body, iron is bound mainly to transferrin and lactoferrin. Many bacteria deal with iron limitation by the secretion of siderophores, which are small organic compounds that bind iron very efficiently. The Fe31-siderophore complex is bound to specific receptors on the bacterial cell surface and internalized. The transport across the outer membrane requires energy, which is provided in Escherichia coli by the inner membrane protein TonB.FrpB is another iron-limitation inducible outer membrane protein of Neisseria meningitides. Its function is unknown. Previously, we have raised monoclonal antibodies against this protein, most of which appeared to be bactericidal in an in vitro assay with human complement. Here we describe the topology and 3D structure of a novel antigen which was discovered by mining the bacterial genome and that is very effective in inducing bactericidal antibodies. This antigen is a very good candidate for inclusion in universal vaccines against N.meningitidis.

Early transcriptomic response to Fe supply in Fe-deficient tomato plants is strongly influenced by the nature of the chelating agent.

BackgroundIt is well known that in the rhizosphere soluble Fe sources available for plants are mainly represented by a mixture of complexes between the micronutrient and organic ligands such as carboxylates and phytosiderophores (PS) released by roots, as well as fractions of humified organic matter. The use by roots of these three natural Fe sources (Fe-citrate, Fe-PS and Fe complexed to water-extractable humic substances, Fe-WEHS) have been already studied at physiological level but the knowledge about the transcriptomic aspects is still lacking.ResultsThe 59Fe concentration recorded after 24 h in tissues of tomato Fe-deficient plants supplied with 59Fe complexed to WEHS reached values about 2 times higher than those measured in response to the supply with Fe-citrate and Fe-PS. However, after 1 h no differences among the three Fe-chelates were observed considering the 59Fe concentration and the root Fe(III) reduction activity. A large-scale transcriptional analysis of root tissue after 1 h of Fe supply showed that Fe-WEHS modulated only two transcripts leaving the transcriptome substantially identical to Fe-deficient plants. On the other hand, Fe-citrate and Fe-PS affected 728 and 408 transcripts, respectively, having 289 a similar transcriptional behaviour in response to both Fe sources.ConclusionsThe root transcriptional response to the Fe supply depends on the nature of chelating agents (WEHS, citrate and PS). The supply of Fe-citrate and Fe-PS showed not only a fast back regulation of molecular mechanisms modulated by Fe deficiency but also specific responses due to the uptake of the chelating molecule. Plants fed with Fe-WEHS did not show relevant changes in the root transcriptome with respect to the Fe-deficient plants, indicating that roots did not sense the restored cellular Fe accumulation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2331-5) contains supplementary material, which is available to authorized users.

Iron deficiency in barley plants: phytosiderophore release, iron translocation, and DNA methylation

All living organisms require iron (Fe) to carry out many crucial metabolic pathways. Despite its high concentrations in the geosphere, Fe bio-availability to plant roots can be very scarce. To cope with Fe shortage, plants can activate different strategies. For these reasons, we investigated Fe deficient Hordeum vulgare L. plants by monitoring growth, phytosiderophores (PS) release, iron content, and translocation, and DNA methylation, with respect to Fe sufficient ones. Reductions of plant growth, roots to shoots Fe translocation, and increases in PS release were found. Experiments on DNA methylation highlighted significant differences between fully and hemy-methylated sequences in Fe deficient plants, with respect to Fe sufficient plants. Eleven DNA bands differently methylated were found in starved plants. Of these, five sequences showed significant alignment to barley genes encoding for a glucosyltransferase, a putative acyl carrier protein, a peroxidase, a β-glucosidase and a transcription factor containing a Homeodomin. A resupply experiment was carried out on starved barley re-fed at 13 days after sowing (DAS), and it showed that plants did not recover after Fe addition. In fact, Fe absorption and root to shoot translocation capacities were impaired. In addition, resupplied barley showed DNA methylation/demethylation patterns very similar to that of barley grown in Fe deprivation. This last finding is very encouraging because it indicates as these variations/modifications could be transmitted to progenies.

Effects of terbuthylazine on phytosiderophores release in iron deficient barley

One of the main purposes of modern agriculture is to raise crop production by means of a proper application of herbicides. Nonetheless, the use of herbicides is causing some concerns associated to their persistence and accumulation in the environment. Notwithstanding the relevance of these aspects, little or no attention has been paid to the interferences that these chemicals and their residues can exert on iron (Fe) mineral nutrition of plants. To this purpose, we studied the effect of terbuthylazine (TBA) on the Fe-acquisition processes of Fe-deficient barley plants, by investigating some aspects related to phytosiderophores (PS) exudation and sulfur (S) metabolism. Results showed that plant growth, chlorophyll content expressed as SPAD index, PS release and the expression of genes involved in their secretion, uptake and biosynthesis were negatively affected. This response was associated with reduced cysteine concentrations, and it suggests that the TBA interferences on Fe-acquisition in barley are the consequence of the induced changes in S metabolism.

Amélioration de la biodégradation du biphényle par Rhodococcus erythropolis t902.1 en présence de Fe2O3 et de nanoparticules de fer encapsulées dans un xérogel de silice

In this work, the effect of iron oxide particles Fe2O3 and iron nanoparticles encapsulated in a porous silica matrix (xerogel Fe/SiO2) was investigated on biphenyl biodegradation by the strain Rhodococcus erythropolis T902.1. After 18 days of incubation biodegradation yields of 75% and 85% were achieved respectively in presence of non-autoclaved or autoclaved xerogel Fe/SiO2at 10-5 M iron. These results are 42 and 60% higher than in standard conditions without nanoparticles. They suggest that the autoclave procedure lead to the release of some iron less anchored in the silica matrix. This study highlights that siderophore production byRhodococcus erythropolis T902.1 would be related to the presence of iron nanoparticles in the culture. It suggests that the production of these strong chelating compounds decreases with increase of iron release from xerogel Fe/SiO2. Moreover, most of the surfactants synthesized by Rhodococcus erythropolis T902.1 which are glycolipids containing trehalose (hexose),would be linked to cell surface and not excreted in the culture medium; the biomass hexose content also increased by 85% in presence of iron nanoparticles. Dans ce travail, l’effet de particules d’oxyde de fer Fe2O3 et de nanoparticules de fer encapsulées dans des particules poreuses de silice (xérogel Fe/SiO2) a été étudié sur la biodégradation du biphényle par la souche Rhodococcus erythropolis T902.1. Les pourcentages de biodégradation après 18 jours d’incubation en présence du xérogel Fe/SiO2 à 10-5 M en fer atteignent 75 % et 85 % respectivement pour les conditions sans ou après autoclavage ; c’est-à-dire 42 et 60 % de dégradation supplémentaire par rapport aux conditions standards sans xérogel Fe/SiO2. L’impact dû à l’autoclavage serait directement associé à la libération d’une certaine quantité de fer moins bien ancré dans la matrice de silice. Cette étude a jeté la lumière sur la liaison entre la sécrétion de sidérophores par Rhodococcus erythropolis T902.1 et la présence de nanoparticules de fer dans le milieu de culture. Elle suggère une diminution de la sécrétion de sidérophores avec l’augmentation de la quantité d’ions ferriques mobilisés à partir du xérogel Fe/SiO2. Finalement, la majorité des surfactants glycolipidiques contenant du trehalose (hexose) produits par Rhodococcus erythropolis T902.1sont liés à la surface de la cellule et ne sont pas excrétés dans le milieu de culture ; leur concentration a augmenté de 85 % en présence de nanoparticules de fer.

Iron allocation in leaves of Fe-deficient cucumber plants fed with natural Fe complexes.

Iron (Fe) sources available for plants in the rhizospheric solution are mainly a mixture of complexes between Fe and organic ligands, including phytosiderophores (PS) and water-extractable humic substances (WEHS). In comparison with the other Fe sources, Fe-WEHS are more efficiently used by plants, and experimental evidences show that Fe translocation contributes to this better response. On the other hand, very little is known on the mechanisms involved in Fe allocation in leaves. In this work, physiological and molecular processes involved in Fe distribution in leaves of Fe-deficient Cucumis sativus supplied with Fe-PS or Fe-WEHS up to 5 days were studied combining different techniques, such as radiochemical experiments, synchrotron micro X-ray fluorescence, real-time reverse transcription polymerase chain reaction and in situ hybridization. In Fe-WEHS-fed plants, Fe was rapidly (1 day) allocated into the leaf veins, and after 5 days, Fe was completely transferred into interveinal cells; moreover, the amount of accumulated Fe was much higher than with Fe-PS. This redistribution in Fe-WEHS plants was associated with an upregulation of genes encoding a ferric(III) -chelate reductase (FRO), a Fe(2+) transporter (IRT1) and a natural resistance-associated macrophage protein (NRAMP). The localization of FRO and IRT1 transcripts next to the midveins, beside that of NRAMP in the interveinal area, may suggest a rapid and efficient response induced by the presence of Fe-WEHS in the extra-radical solution for the allocation in leaves of high amounts of Fe. In conclusion, Fe is more efficiently used when chelated to WEHS than PS and seems to involve Fe distribution and gene regulation of Fe acquisition mechanisms operating in leaves.